SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13G

             INFORMATION STATEMENT PURSUANT TO RULES 13d-1 AND 13d-2
                  UNDER THE SECURITIES AND EXCHANGE ACT OF 1934
                             (Amendment No.   4   )*


                                Foster (L.B.) Co.
- --------------------------------------------------------------------------------
                                (Name of Issuer)




                                  Common Stock
- --------------------------------------------------------------------------------
                         (Title of Class of Securities)


                                    350060109
- --------------------------------------------------------------------------------
                                 (CUSIP Number)



- -----------------------------

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



                        (Continued on following page(s))
                                Page 1 of 8 Pages



CUSIP No. 350060109                    13G              Page  2  of  8  Pages
- ----------------------                               ---------------------------

- --------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

               The TCW Group, Inc.
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                        (a)  / /
                                                                        (b)  /X/
- --------------------------------------------------------------------------------
3    SEC USE ONLY

- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

          Nevada corporation
- --------------------------------------------------------------------------------
           NUMBER OF               5    SOLE VOTING POWER
            SHARES                                                     924,500
         BENEFICIALLY              ---------------------------------------------
           OWNED BY                6    SHARED VOTING POWER
             EACH                                                          -0-
           REPORTING               ---------------------------------------------
            PERSON                 7    SOLE DISPOSITIVE POWER
             WITH                                                      924,500
                                   ---------------------------------------------
                                   8    SHARED DISPOSITIVE POWER
                                                                           -0-
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
                                                                       924,500
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
     CERTAIN SHARES*
                                                                           / /
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
      9.3% (see response to Item 4)
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*
                                      HC/CO
- --------------------------------------------------------------------------------



                    *SEE INSTRUCTIONS BEFORE FILLING OUT!



CUSIP No. 350060109                    13G              Page  3  of  8  Pages
- ----------------------                               ---------------------------

- --------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

               Robert Day
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                        (a)  / /
                                                                        (b)  /X/
- --------------------------------------------------------------------------------
3    SEC USE ONLY

- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

          United States Citizen
- --------------------------------------------------------------------------------
           NUMBER OF               5    SOLE VOTING POWER
            SHARES                                                     924,500
         BENEFICIALLY              ---------------------------------------------
           OWNED BY                6    SHARED VOTING POWER
             EACH                                                          -0-
           REPORTING               ---------------------------------------------
            PERSON                 7    SOLE DISPOSITIVE POWER
             WITH                                                      924,500
                                   ---------------------------------------------
                                   8    SHARED DISPOSITIVE POWER
                                                                           -0-
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
                                                                       924,500
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
     CERTAIN SHARES*
                                                                           / /
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
      9.3% (see response to Item 4)
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*7
                                      HC/IN
- --------------------------------------------------------------------------------



                    *SEE INSTRUCTIONS BEFORE FILLING OUT!



                                                               Page 4 of 8 Pages

Item 1(a).     Name of Issuer:

               Foster (L.B.) Co.

Item 1(b).     Address of Issuer's Principal Executive Offices:

               415 Holiday Dr.
               Pittsburgh, PA 15220-2729

Item 2(a).     Name of Persons Filing:
Item 2(b).     Address of Principal Business Office:
Item 2(c).     Citizenship:

               The TCW Group, Inc.
               865 South Figueroa Street
               Los Angeles, CA 90017
               (Nevada Corporation)

               Robert Day
               200 Park Avenue, Suite 2200
               New York, New York 10166
               (United States Citizen)

Item 2(d).     Title of Class of Securities:

               Common Stock

Item 2(e).     CUSIP Number:

               350060109



                                                               Page 5 of 8 Pages

Item 3.        If this statement is filed pursuant to Rules 13d-1(b), or
               13d-2(b), check whether the person filing is a:


     (a)       [ ]  Broker or Dealer registered under Section 15 of the Act:

                         Not applicable

     (b)       [ ]  Bank as defined in Section 3(a)(6) of the Act:

                         Not applicable

     (c)       [ ]  Insurance Company as defined in Section 3(a)(19) of the Act:

                         Not applicable

     (d)       [ ]  Investment Company registered under Section 8 of the
                    Investment Company Act:

                         Not applicable

     (e)       [ ]  Investment Adviser registered under Section 203 of the
                    Investment Advisers Act of 1940:

                         Not applicable

     (f)       [ ]  Employee Benefit Plan, Pension Fund which is subject to the
                    provisions of the Employee Retirement Income Security Act of
                    1974 or Endowment Fund (SEE 13d-1(b)(1)(ii)(F)):

                         Not applicable

     (g)       [X]  Parent Holding Company, in accordance with Rule
                    13d-1(b)(ii)(G) (SEE Item 7):

                         The TCW Group, Inc.
                         Robert Day (individual who may be deemed to control The
                             TCW Group, Inc. and other holders of the Common
                             Stock of the issuer)

     (h)       [ ]  Group, in accordance with Rule 13d-1(b)(1)(ii)(H):

                         Not applicable.



                                                               Page 6 of 8 Pages

Item 4.        Ownership **

     THE TCW GROUP, INC.

               (a)  Amount beneficially owned: 924,500

               (b)  Percent of class: 9.3%

               (c)  Number of shares as to which such person has:

                    (i)   Sole power to vote or to direct the vote:
                            924,500

                    (ii)  Shared power to vote or to direct the vote:   none.

                    (iii) Sole power to dispose or direct the disposition of:
                            924,500

                    (iv)  Shared power to dispose or to direct the disposition
                    of:  none.

     ROBERT DAY

               (a)  Amount beneficially owned: 924,500

               (b)  Percent of class: 9.3%

               (c)  Number of shares as to which such person has:

                    (i)   Sole power to vote or to direct the vote:
                            924,500

                    (ii)  Shared power to vote or to direct the vote: none.

                    (iii) Sole power to dispose or direct the disposition of:
                            924,500

                    (iv)  Shared power to dispose or to direct the disposition
                    of:  none.

- ----------------------

**  The filing of this Schedule 13G shall not be construed as an admission that
the reporting person or any of its affiliates is, for the purposes of Section
13(d) or 13(g) of the Securities Exchange Act of 1934, the beneficial owner of
any securities covered by this Schedule 13G.  In addition, the filing of this
Schedule 13G shall not be construed as an admission that the reporting person or
any of its affiliates is the beneficial owner of any securities covered by this
Schedule 13G for any other purposes than Section 13(d) of the Securities
Exchange Act of 1934.



                                                               Page 7 of 8 Pages

Item 5.        Ownership of Five Percent or Less of a Class.

                    Not applicable.

Item 6.        Ownership of More than Five Percent on Behalf of Another Person.

               Various persons other than as described in Item 4, including the
               TCW Value Added Trust, have the right to receive or the power to
               direct the receipt of dividends from, or the proceeds from the
               sale of, the Common Stock of Foster (L.B.) Co.

Item 7.        Identification and Classification of the Subsidiary Which
               Acquired the Security Being Reported on by the Parent Holding
               Company.

               SEE Exhibit A.

Item 8.        Identification and Classification of Members of the Group.

               Not applicable. SEE Exhibits A and B.

Item 9.        Notice of Dissolution of Group.

               Not applicable.

Item 10.       Certification.

          Because this statement is filed pursuant to Rule 13d-1(b), the
          following certification is included:


          By signing below I certify that, to the best of my knowledge and
          belief, the securities referred to above were acquired in the ordinary
          course of business and were not acquired for the purpose of and do not
          have the effect of changing or influencing the control of the issuer
          of such securities and were not acquired in connection with or as a
          participant in any transaction having such purpose or effect.



                                                               Page 8 of 8 Pages


                                    SIGNATURE


               After reasonable inquiry and to the best of my knowledge and
belief, I certify that the information set forth in this statement is true,
complete and correct.


Dated this 12th day of February, 1997.


                                        The TCW Group, Inc.


                                        By:  /s/ Mohan V. Phansalkar
                                             -----------------------
                                             Mohan V. Phansalkar
                                             Authorized Signatory



                                        Robert Day


                                        By:  /s/ Mohan V. Phansalkar
                                             -----------------------
                                             Mohan V. Phansalkar
                                             Under Power of Attorney dated
                                             January 30, 1996, on File with
                                             Schedule 13G Amendment Number 1 for
                                             Matrix Service Co. dated January
                                             30, 1996.



                                    EXHIBIT A


                 RELEVANT SUBSIDIARIES OF PARENT HOLDING COMPANY

PART A: TCW ENTITIES

PARENT HOLDING COMPANY:

             The TCW Group, Inc.

             Robert Day (an individual who may be deemed to control The TCW
             Group, Inc.)


RELEVANT SUBSIDIARIES THAT ARE PERSONS DESCRIBED IN RULE 13d-1(b):

       (i)   Trust Company of the West, a California corporation and a bank as
       defined in Section 3(a)(6) of the Securities Exchange Act of 1934.

       (ii)  TCW Asset Management Company, a California corporation and an
       Investment Adviser registered under Section 203 of the Investment
       Advisers Act of 1940.

Note:        No Common Stock of Foster (L.B.) Co. is held directly by The TCW
             Group, Inc.  Other than the indirect holdings of The TCW Group,
             Inc. no Common Stock of Foster (L.B.) Co. is held directly or
             indirectly by Robert Day, an individual who may be deemed to
             control The TCW Group, Inc.

PART B: NON TCW ENTITIES

PARENT HOLDING COMPANY:

             Robert Day (an individual who may be deemed to control the holders
             described below which are not subsidiaries of The TCW Group, Inc.)

RELEVANT SUBSIDIARIES THAT ARE PERSONS DESCRIBED IN
RULE 13d-1(b):

             Oakmont Corporation, a California corporation and an Investment
             Adviser registered under Section 203 of the Investment Advisers Act
             of 1940.

             Cypress International Partners Limited, a British Virgin Islands
             corporation and an Investment Adviser registered under Section 203
             of the Investment Advisers Act of 1940.




                                       A-1


                                    EXHIBIT B

                             JOINT FILING AGREEMENT


          The undersigned acknowledge and agree that the foregoing statement on
Schedule 13G is filed on behalf of each of the undersigned and that all
subsequent amendments to this statement on Schedule 13G shall be filed on behalf
of each of the undersigned without the necessity of filing additional joint
acquisition statements.  The undersigned acknowledge that each shall be
responsible for the timely filing of such amendments, and for the completeness
and accuracy of the information concerning him or it contained therein, but
shall not be responsible for the completeness and accuracy of the information
concerning the other, except to the extent that he or it knows or has reason to
believe that such information is accurate.


Dated: February 12, 1997


                                        The TCW Group, Inc.


                                        By:  /s/ Mohan V. Phansalkar
                                             -----------------------
                                             Mohan V. Phansalkar
                                             Authorized Signatory



                                        Robert Day


                                        By:  /s/ Mohan V. Phansalkar
                                             -----------------------
                                             Mohan V. Phansalkar
                                             Under Power of Attorney dated
                                             January 30, 1996, on File with
                                             Schedule 13G Amendment Number 1 for
                                             Matrix Service Co. dated January
                                             30, 1996.





                                       B-1